This invention relates to sliding window assemblies. Common sliding windows include either a fixed sash and a movable sash side-by-side, or a pair of movable sashes also side-by-side. Without regard to type, the common sliding window has a negative reputation for being poor in thermal performance, difficult to open and close, most difficult to clean, and for being a security risk. The windows tend to leak frigid winter air, become icy, and in even good weather, resist all but aggressive manual movement. The sashes of some such windows can only be cleaned by complete removal of the sashes from the window frame. Most such windows include only locks between the two sashes.